The carbonylation of olefins at high temperatures and pressures produces after hydrolysis of the acid-catalyst complex, organic acids of a heavily branched nature, i.e., neo acids, which are totally substituted at the .alpha.-carbon and also known as trialkyl acetic acids. The difficulty associated with the preparation of esters of neo acids is well known as is the property of enhanced hydrolytic stability of these esters once prepared. The difficulty in preparation and the enhanced hydrolytic stability of these neo acid esters may, in theory, be attributed to either a steric or an ionization effect. It appears that the rate of esterification decreases sharply as the degree of acid chain branching increases. A paper by Coopersmith et al entitled "Preparation of Hydrolytic Stability of Trialkylacetic Acid Esters", I&EC, 5, No. 1, pp. 46-49 (March 1966) reports that on a laboratory basis, esters of neo-acids can be produced in high yields with a homogeneous acid catalyst (p-toluene sulfonic acid, sulfuric acid) and a water entrainer. However, the reported heterogeneous sulfonic acid polymer catalyst (Amberlyst IR120H, sold by Rohm & Haas, Philadelphia, Pa., provoked a very poor yield of neo acid ester.
Coopersmith et al in U.S. Pat. No. 4,125,549 teach an improvement in the preparation of a neo decanoic acid ester (isooctyl neodecanoate) in the presence of a heterogeneous sulfonic acid catalyst by steam stripping the distilled ester product until the sulfur content is less than 20 ppm and in the presence of an oxidant. The above-taught process required extensive purification procedures to avoid the contamination inherent with the homogeneous sulfonic acid catalyst.
In a more difficult esterification reaction of neo acids than that of Coopersmith et al, Whyte (in U.S. Pat. No. 3,579,548) teaches the preparation of glycerol esters in the presence of both toluene sulfonic acid (Examples I, II and IV) and sulfuric acid (Example III); however, complex purification and/or separation procedures for separation of said ester from the homogeneous catalyst are required.
Finally, U.S. Pat. No. 3,590,073 teaches the use of macro-reticular sulfonic acid cationic exchange resins for catalysis of the esterification of tertiary alcohols with organic carboxylic acids having from 2 to 20 carbon atoms with relatively low yields. With sterically hindered alcohols, the presence of a heterogeneous sulfonic acid type cationic exchange resin appears to inhibit the usual tendency of said alcohols to dehydrate and produce an olefin which subsequently polymerizes in the presence of an acid catalyst, i.e. an undesirable reaction competing with esterification but not one of relevance for the esterification of trialkylacetic acid.
It is an object of this invention to overcome the foregoing disadvantages and/or teachings of the prior art.
It is a further object of this invention to provide an improved method for the esterification of neo-acids in high yield and high purity.